Do-it-yourself Ovulation Tests Put Thermometers To Shame

''Hurry home, dear, my temperature just dropped!'' You know the scene: The frantic wife calls her husband at the office to hurry home for what they hope will be a productive, if quick, interlude.

To conceive, a woman must ovulate, producing an egg that is available for fertilization. Thus, she must know when, and if, she's ovulating and schedule intercourse accordingly.

In the past, couples had to rely on basal body temperature graphs to predict the magic moment of ovulation. Every morning before a woman got out of bed, she took her temperature and recorded the results on a graph.

This practice was necessary because just before ovulation a woman's basal body temperature drops a little, then rises, averaging about six-tenths of a degree higher in the last two weeks of the menstrual cycle. Theoretically, a woman could determine when she would ovulate by watching the rise and fall of her temperature.

Unfortunately, studies showed that this method is accurate only 17 to 18 percent of the time. And there's no margin for error. If a woman oversleeps one morning and forgets to take her temperature, it can throw off the chart for an entire month.

But today there's a more accurate way -- easy-to-use home ovulation kits that predict with 86 to 93 percent accuracy (depending on individual manufacturers' claims) when ovulation will occur in the 22 to 44 hours after the test.

Home ovulation kits are used to test urine for the presence of luteinizing hormone (LH), which is produced by the pituitary gland. When the ovary has been subjected to this hormone for a number of hours, ovulation occurs.

The kits are available at pharmacies and supermarkets. They're so accurate in pinpointing ovulation that gynecologists use them to schedule other tests and to check the effectiveness of prescribed fertility drugs.

Unlike home pregnancy tests, which have a lower accuracy rate than those performed in a lab, home ovulation tests are highly accurate both at home and in the lab. Consumer studies of home ovulation tests conducted by manufacturers indicate that the tests are 93 percent effective when performed by the average consumer. Naturally, it would be more reassuring if the consumer tests had been conducted by independent research firms rather than manufacturers, but this method is better than none.

Furthermore, because home ovulation kits test specifically for LH levels, test results are not affected by cold medications or vitamins, as home pregnancy tests may be. As an added assurance, all of the companies selling ovulation predictor kits have toll-free numbers you can call for free advice, usually from a registered nurse.

On the down side, home ovulation tests are not 100 percent accurate and they're expensive, ranging from $20 to $70, depending on how many months of use each kit provides.